This invention relates to an apparatus for measuring the distribution of non-linear parameters of an ultrasonic wave medium, and particularly to a measuring apparatus in the system for measuring the space distribution of the physical characteristics of an ultrasonic wave medium such as a living tissue, etc., wherein the space distribution of the non-linear parameters is measured as a characteristic value of the medium and moreover wherein such space distribution is visualized at a high speed and with ease as required, by making use of such non-linear characteristics as that the sound velocity is constant with respect to variation in sound pressure in the primary approximation, but is proportional to the sound pressure in the secondary approximation. Moreover, this invention relates particularly to an apparatus wherein said non-linear parameters can be measured by the reflection method instead of the so-called transmission method.
The principle of the non-linear visualization method used in this invention is described in detail in the Japanese Patent Application No. 58-399073 (U.S. Ser. No. 587,522, filed Mar. 8, 1984 and now U.S. Pat. No. 4,566,460) and Japanese Patent Application No. 58-119100. In the former case, the non-linear parameter B/A defined below has been obtained at high speed on the measuring ultrasonic beam scanning line by causing a comparatively low frequency flat pulse for pumping to orthogonally cross a comparatively high frequency continuous ultrasonic beam for measurement, and by phase-demodulating the phase-modulated measuring wave by the pumping pulse. In the latter case, almost the same type of pumping pulse is received at almost all parts of the measuring beam, and the effect of eliminating a mechanically large structure can be obtained by providing the pumping pulse in such a way that it is concentric to the measuring beam and travels in the opposite direction as the measuring beam.
However, these methods all employ the transmission method wherein the signal is generated from a transducer for sending a measuring ultrasonic wave which is thereafter received by a transducer for receiving the measuring signal after it passes through the medium to be measured. An attempt to obtain a tomographic image in the actual clinical application has been accompanied by major operating problems, such as being limited only to breasts wherein the observing area can be set between the transducers for, or such as the area to be observed must be scanned with the transducers for measurement by surrounding such area by a water pillow.
Moreover, the ultrasonic wave is reflected from an area having a bone or a cavity, and thereby observation by the transmission method has been difficult.